Acid copper electroplating baths



United States Patent 1 2,950,235 ACID COPPER ELECTROPLATING BATHSWennemar Strauss and Wolf-Dieter Willmund, Dusseldorf-Holthausen,Germany, assignors to Dehydag, Dentsche Hydrierwerke G.m.b.H.,Dusseldorf, Germany, a corporation of Germany No Drawing. Filed Dec. 4,1958, Ser. No. 778,075 Claims priority, application Germany Dec. 17,1957 8 Claims. (Cl. 204-52) This invention relates to acid copperplating baths containing organic compounds as brightening additives. Itmore specifically relates toan electroplating method and the bathstherefore which eliminate anode sludge by the addition or" new additivesto the acid copper plating bath.

Acid copper electroplating baths which are usually operated with organicelectroplating additives often have the disadvantage that they form aconsiderable amount of anode sludge. This sludge consists of finelydispersed, probably oxidized copper particles which also reach theobjects to be copper plated by electrophoresis and thereby considerablyreduce the quality of the copper electrodeposits. The typical blue colorof the acid copper baths is discolored green through the presence ofthese fine particles.

It has been attempted to avoid the formation of the anode sludge byusing specially alloyed (phosphorus-containing) copper anodes. It hasfurther been attempted to eliminate the presence of impurities byconstantly filtering the baths through filter aggregates and/orsurrounding the anodes with filter bags. Despite these measures it isunavoidable that small amounts of colloidal impurities remain in thecopper bath.

It has also been proposed to eliminate the bath impurities by blowingair therethrough or by adding oxidizing agents, such as hydrogenperoxide. By blowing air through the bath the impurities are oxidizedinto copper- II-compounds which are again transformed into coppersulfate by the sulfuric acid in the bath, but this method is notrecommended in most cases, especially if the copper baths are operatedwith wetting agents, because of the strong foam formation.

The addition of hydrogen peroxide leads to the destruction of theimpurities within a short time, but this method has the disadvantagethat it causes the copper electroplates to become brittle and that theusable current density range is greatly reduced. For this reason, if thecopper electroplating bath is regenerated with hydrogen peroxide thebath must be taken out of operation for an extended period of time untilall of the hydrogen peroxide has decomposed.

All of the measures described above make the operation of acid copperelectroplating baths considerably more difficult and require additionalwork or additional apparatus. Moreover, in these methods, it wasunavoidable that some sludge particles deposited with theelectrodeposit.

It is an object of this invention to prevent anode sludge formation inacid copper plating baths.

Another object is to provide an electroplating bath free from colloidalimpurities.

Yet another object is to provide a method and bath for acid copperplating wherein auxiliary measures to maintain purity of the bath suchas filtering, oxidation, special anodes, etc. are unnecessary.

Another object is to provide a method for obtaining a high qualitycopper deposit free from impurities in an acid copper plating bath suchas anode sludge particles.

Another object is to provide an additive compound for acid copperplating baths which maintains the bath in a highly pure state.

compounds.

Patented Aug. 23, 1960 We have now found that all of thesedisadvantageso'f the prior art methods can be avoided and the objects ofour invention achieved by adding to the acid copperelec- ,troplatingbaths organic sulfonic acids containing at least one azido '(triazo)group in the molecule or salts of such The addition of these compoundshas the effect that the baths remain deep blue in color and clear and-donot form asludge throughout their entire period of operativeness, evenif they are operated at high loads, whereas baths which are operatedwithout these additives turn green-after 2-4 a.h./liter acid and aftersome additional time begin to produce anode sludge.

At the same time, the novel products also produce a certain brighteningeffect. The brightness can be .improved by further adding knownbrighteners to the baths. Examples of brighteners which may be used are:thiourea and its derivatives, N-monoand di-substituted dithiocarbamicacid alkyl esters-w-sulfonic acids or their salts,

F 1 Zn R-SO H wherein R is a lower saturated aliphatic hydrocarbonradical or an aromatic hydrocarbon radical, -Z is an azido group and nis a whole number of at least one. I

Examples of organic sulfonic acids having at least one azido group inthe molecule are the following:

.3-azido-propane-sulfonic acid-1 4-azido-butane-sulfonic acid-1l-azido-l,1-dimethylpropane-sulfuric acid-33-azido-2-hydroxy-propane-sulfonic acid-12-azido-3-halo-propane-sulfonic acid-l 2,3-diazido-propane-sulfonicacid-1 2,3-d.iazido-butane-sulfonic acid-l 8-azido-naphthalene-sulfonicacid-1 4-azido-benzene-sulfonic acid Z-(azido-methyl)-benzene-sulfonicacid These compounds may be produced inaccordance with known processes,for example by reacting sultones, such as propane sultone, tolylsultoneand 1,8-naphthylsultone, with hydrazoic acid or its salts (azides) or byreacting hydrazoic acid or its salts with halogen-substituted organicsulfonic acids.

The acids are customarily used in the form of their Water-soluble salts.Inorganic or organic bases, such as the alkali metals, ammonia,dialkylamines or dialkanolamines, may be used as salt formingcomponents.

The compounds according to the present invention are added to the acidcopper electroplating baths in amounts of 0.05-45 gm./liter, preferablyof 0.2-0.8 gm./liter. The operating temperatures of such baths, whichare usually operated within a current density range of 0 to 12.5amp./dm. may vary within wide limits up to about 60 C.

The following examples are set forth to enable persons skilled in theart to better understand and practice the invention. It will beunderstood that there is no intention of limiting the invention to theseexamples.

Examples An acid copper electroplating bath containing 220 gm./ literCuSO 5H O, 60 gm./ liter H 0.05 gin/liter N,N-diethyl-dithiocarbamicacid ethyl ester-w-sodium su1- 3 I fonate as a 'brightener, 0.25gm./liter 1,3-bis-(dibutylamino)-propanol-2 as a ductility-improvingagent, and 1 gm./ liter of the reaction product of dodecyl alcohol and.8 mols ethylene oxide as a wetting agent, was modified with: 0.5 gm./liter w-azido-propane-sodium sulfonate. 'Fullbright copper,electroplates were obtained upon elec troplating objects made of brass,bronze, iron or steel therein: The bath can-be operated withinatemperature range of about 15 to about 50 C. The useable currentdensities at 15 C. lie between and 4.5 amp./ dmQ at 25 C. between 0 and8'amp./dm. and at 50 '0." between 1 and 12.5 amp./dm. The copperelectro- "plating bath did not discolor and retained its blue color,even after prolonged periods of'operation. Sludge'for- "mation at thecopper anodes did not occur; "Neither recycling pumps, filters, or anodebags were required. Alsludge free deposit of copper was obtained.

' Without the addition of w-azido-propane-sodium sul- -fonate the bathmust be continuously recycled and filtered. Despite filtration, acertain amount of reduction in the brightness may occur, which isundesirable;

In place of w-azido-propane-sodium sulfonate the following compoundswere used according to the examples 'above in amounts of 0.2 to 0.8gm./liter with comparable results:

3-azido-2-hydroxy-propane-sulfonie acid-1.2-azido-3-halo-propane-sulfonic acid-1 2,3-diazido-propane-sulfonicVacid-1 '3-azido-butane-sulfonic acid-1 8-azido-naphthalene-sulfonicacid-1 4-azido-benzene-sulfonic acid or their water-soluble salts.

While we have disclosed certain specific embodiments of our invention,we wish it to be understood that these are not intended to belimitative, and that various changes and modifications may be madeWithout departing from the spirit of our invention or the scope of theappended claims.

We claim:

1. An acid copper electroplating bath for producing copperelectrodeposits of high quality free from anode sludge, comprising anaqueous acid solution of a copper salt and a' compound selected from thegroup consisting of compounds having the following general structuralformula:

znrR-sonn group consisting of compounds having the following generalstructural formula:

Z R--SO H] I and water soluble salts thereof, wherein R is a radicalselected from the group consisting of lower aliphatic saturatedhydrocarbon and aromatic hydrocarbon radi- -cals, Z is an azido groupand n is a whole number of at least one, said compound being added in anamount suificient to prevent sludge formation.

3. An acid copper electroplating bath for producing copperelectrodeposits of high quality free from anode sludge comprising anaqueous acid solution of a copper salt; a brightening agent selectedfrom the group consisting of N-monoand di-substituted dithiocarbamic.acid alkyl ester-w-sulfonic acids and their salts, and

1,3,5 triazine 2,4,6 4 tris (mercapto alkane sulfonic acids), the amountof said brightening agent being sulficient to elfect said brightening;and a compound selected and water soluble salts thereof, wherein R is aradical selected from the group consisting of lower aliphatic saturatedhydrocarbons and aromatic hydrocarbon radicals, Z is an'azido group andn is a whole number of at least one, said compound being added in anamount suflicient to prevent sludge formation.

4. An acid copper electroplating bath for producing copperelectrodeposits of high quality free from anode sludge comprising anaqueous acid solution of copper sulfate, at least 0.01 gm./liter of N,Ndiethyl dithiocarbarnic acid ethyl 'ester-w-sodium sulfonate and 0.05 to4.5 gm./ liter w-azido-propane sodium sulfonate.

5. A method for preventing anode sludge formation and for maintainingthepurity of an acid copper plating bath which comprises the step ofadding to said bath a compound selected from the group consisting ofcompounds having the following general structural formula:

and water soluble salts thereof, wherein R is a radical selected fromtheg roup consisting of lower saturated aliphatic hydrocarbon andaromatic hydrocarbon radicals, Z is an azido group and n is a'wh'olenumber of at least one, said compound being added in an amountsuflicient to prevent sludge formation. 7

6. A method for preventing anode sludge formation and for maintainingthe purity of an acid' copper pla t ing bath which comprises the step ofadding to said bath a compound selected from the group consisting ofcompounds having the following general structural formula:

and water soluble salts thereof, wherein R is a radical selected fromthe group consisting of lower saturated aliphatic hydrocarbon andaromatic hydrocarbon radicals,'Z is an azido group and n is a wholenumber of at least one, said compound being added in an amountsufiicient to prevent sludge formation.

7. A method for preventing anode sludge formation and for maintainingthe purity of an acid copper plating bath and the brightness ofelectrodeposits obtained therefrom, which comprises the step of addingto said bath brightening agents selected from the group consisting ofN-monoand di-substituted dithiocarbamic acid alkyl ester-w-sulfonicacids and their salts, and 1,3,5-triazine-'2,4,6-tris-(mercapto-alkane-sulfonic acids), the amount of saidbrightening agent being suflicient to effect said brightening; and acompound selected from the group consisting of compounds having thefollowing general structural formula:

Z ERSO H] V and water soluble salts thereof, wherein R is a radicalselected from the group consisting of lower saturated ahphatichydrocarbon and aromatic hydrocarbon radicals, Z is an azido group and'n is a whole number of fate and at least 0.01 gm./liter ofN,N-diethyl-dithiocarbamic'acid ethyl ester-w-sodium sulfonate as abrightening agent, the step of adding to said bath from 0.05 to 4.5gm./liter of w-azido-propane-sodium sulfonate.

References Cited in the file of this patent UNITED STATES PATENTS2,849,352 Kirstahler et a1 1 Aug. 26, 1958 UNITED STATES PATENT orricrCERTEFIATN 6F CORRECTION Patent No. 2,950,235 August 23, 1960 WennemarStrauss et a1.

It is Hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 2, line 11 for -a.h.,/liter acid read amperehours per liter ofacid bath column 4, line 26, for "theg roup read the group Signed andsealed this 8th day of August 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

1. AN ACID COPPER ELECTROPLATING BATH FOR PRODUCING COPPERELECTRODEPOSITS OF HIGH QUALITY FREE FROM ANODE SLUDGE, COMPRISING ANAQUEOUS ACID SOLUTION OF A COOPER SALT AND A COMPOUND SELECTED FROM THEGROUP CONSISTING OF COMPOUNDS HAVING THE FOLLOWING GENERAL STRUCTURALFORMULA: